The invention relates to an optical fiber fixing structure for fixing a coated optical fiber such as a coated plastic optical fiber to an optical fiber fixture such as a ferrule or connector.
In recent years, with the realization of faster signal processing for personal computers or LANs (local area networks) and the diversification of services, the realization of faster signal transmission rates has been proceeding. Additionally, with the dramatic development of computerization in vehicles, for example, displaying a vehicle location on a map using a car navigation system and management for solving traffic congestion or the like utilizing the ITS (Intelligent Transport Systems) are conducted. With such computerization, communication information throughput such as data, image and voice in vehicles has been increasing.
As described above, when the realization of faster signal transmission rates and the increased communication information throughput proceed, an influence of noises in communications has been growing. On this account, plastic optical fibers (coated plastic optical fibers) capable of reducing the influence of noises have been used in signal transmission lines.
Generally, the plastic optical fiber is provided with a sheath such as nylon. As forms of sheaths, there is multilayer sheath where a first sheath such as nylon is disposed around the outer periphery of a plastic optical fiber strand and a second sheath such as nylon is further disposed around the outer periphery of the first sheath. When the plastic optical fiber is used as a high bit-rate signal transmission line, for example, in a state that the sheath at the connection end face side is removed to expose the plastic optical fiber strand or the second sheath or more is removed to expose the first sheath, this exposed portion and the coated portion are inserted and fixed to an optical fiber fixture such as a ferrule or connector. The optical fiber fixture is formed with a proper optical fiber insertion hole.
As one example of the fixing structure for the aforesaid plastic optical fiber, a structure is known that a plastic optical fiber is inserted into an optical fiber insertion hole of a metal or a resin ferrule and the plastic optical fiber is fixed to the ferrule with an adhesive such as an epoxy resin.
Additionally, a structure is proposed that a plastic optical fiber is fixed to a ferrule by crimping the ferrule in a state that the plastic optical fiber is inserted into an optical fiber insertion hole of a metal ferrule.
Furthermore, as another example, a structure is proposed that in a state that a plastic optical fiber is inserted into an optical fiber insertion hole of a ferrule made of a transparent resin, laser light is irradiated from the outside of the ferrule to weld the resin of the ferrule with a sheath resin of the plastic optical fiber and thereby the plastic optical fiber is fixed to the ferrule.
Moreover, as proposed in Japanese Utility Model Laid-Open (No. 42836/1992), a structure is proposed that a plastic optical fiber (coated plastic optical fiber) 3 is fixed to a ferrule using a metal member 15 as shown in FIG. 6A, for example.
This fixing structure is that the plastic optical fiber 3 inserted into an optical fiber insertion hole of the ferrule is supported by the metal member 15 and is fixed and prevented from falling off from the ferrule so that the plastic optical fiber 3 does not fall off from the ferrule even though tensility is applied the plastic optical fiber 3 in the longitudinal direction thereof.
FIG. 6B depicts a diagram illustrating a state of fixing the plastic optical fiber 3 by the metal member 15 that is seen from the under side of the plastic optical fiber 3. As shown in FIG. 6B, the support for the plastic optical fiber 3 by the metal member 15 is conducted in which clamping parts 16 of the metal member 15 provide point contacts at each supporting position with a space in the longitudinal direction of the plastic optical fiber 3.
However, when the structure of fixing the optical fiber to the ferrule using the adhesive such as the epoxy resin as described above, there has been a problem that handling the adhesive is troublesome and curing the adhesive takes time.
Additionally, when the fixing structure of crimping the metal ferrule is adapted, the ferrule must be made of metal and there has been a problem of high costs because metal is more expensive than plastic.
Furthermore, when the fixing structure is adapted that the ferrule resin is welded with the sheath resin of the plastic optical fiber using laser light, there has been a problem that equipment expenses are required because laser irradiation facilities are needed.
Moreover, when the fixing structure shown in FIGS. 6A and 6B is adapted, the metal member 15 might damages the core of the plastic optical fiber 3 in case where the dimensional accuracy of the metal member 15 is not controlled strictly. Once the core is damaged, there has been a problem that a transmission loss of the plastic optical fiber 3 is increased.
In one aspect of the invention, it is to provide an optical fiber fixing structure capable of fixing a coated optical fiber such as a plastic optical fiber to an optical fiber fixture easily with low costs and causing no increase in a transmission loss of the coated optical fiber.
The invention is to provide an optical fiber fixing structure having the following configuration. That is, an optical fiber fixing structure of the invention for fixing a coated optical fiber to an optical fiber fixture, the optical fiber fixing structure is characterized in that the optical fiber fixture is formed with an optical fiber insertion hole penetrating from a tip end side thereof to a back end side and an opening communicating from a side of the optical fiber fixture to the aforesaid optical fiber insertion hole, wherein the coated optical fiber is inserted into the aforesaid optical fiber insertion hole, an optical fiber fixing component having optical fiber clamping parts facing each other is inserted and fit to the aforesaid opening as clamping tip end sides of the aforesaid optical fiber clamping parts are faced to a side of the aforesaid coated optical fiber, the coated optical fiber is clamped from both sides by the optical fiber fixing component as an outer periphery of the aforesaid coated optical fiber is clamped between inner wall surfaces of the optical fiber clamping parts facing each other of the aforesaid optical fiber fixing component, outer surfaces of the optical fiber clamping parts of the aforesaid optical fiber fixing component are pressure welded with inner wall surfaces of the opening of the aforesaid optical fiber fixture, and the aforesaid coated optical fiber is fixed and prevented from falling off from the aforesaid optical fiber fixture.
As one exemplary embodiment, a space of the optical fiber clamping parts of the optical fiber fixing component is formed smaller than the outer diameter of the coated optical fiber and the aforesaid optical fiber clamping parts are formed to be optical fiber pressing parts for clamping and holding the coated optical fiber from both sides.
As one example, the optical fiber fixing component is a gutter-like component having a U-shaped cross section, where the optical fiber clamping parts are extended from both sides of a base part and faced each other.
As a preferable example of the fixing structure for the coated optical fiber, it is a unbonded clamping and fixing structure where the coated optical fiber is pressure welded and fixed between the optical fiber clamping parts of the optical fiber fixing component without using an adhesive and the optical fiber fixing component is pressure welded and fixed between the inner wall surfaces of the opening of the optical fiber fixture without using an adhesive.
Preferably, the optical fiber clamping parts of the optical fiber fixing component are formed with bumps and dips in the inner wall surfaces thereof.
The bumps and dips in the inner wall surfaces of the optical fiber clamping parts of the optical fiber fixing component may be formed to have a plurality of fins that are spaced each other and extended slantly in the direction of inserting the optical fiber.
The optical fiber fixture is formed to be a cylindrical ferrule or a connector provided with one or more cylindrical ferrules and the cylindrical bore of the aforementioned cylinder may be the optical fiber insertion hole.
As one example, in the opening of the optical fiber fixture, inner wall surfaces facing to the optical fiber clamping parts of the optical fiber fixing component are formed to be straight surfaces.
The entrance of the opening of the optical fiber fixture may be formed with projecting parts for preventing the optical fiber fixing component from falling off.
Preferably, at least the optical fiber fixing component of the optical fiber fixture and the optical fiber fixing component is formed of plastic.
As one example, the coated optical fiber is a coated plastic optical fiber where a sheath is formed around the outer periphery of a plastic optical fiber strand.